Early Wednesday and/or Thursday morning, temperatures are forecast to drop below freezing in portions of all 50 states, even in normally mild Florida and Hawaii.
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Workers carry snow shovels as snow falls on Nov. 25, 2018, in downtown Kansas City, Mo. A new storm is forecast to wallop the southern tier of the U.S. with snow, ice and rain over the next few days.(Photo: CHARLIE RIEDEL, AP)

A powerful storm that slammed southern California Thursday will crawl across the southern tier of the United States over the next several days, delivering a nasty mix of snow, ice, heavy rain, floods and even a few tornadoes.

Ahead of the storm, Oklahoma Gov. Mary Fallin declared a state of emergency for all 77 counties in her state.

As of midday Thursday, about 20 million people were under some level of weather alert. Many tens of millions more should be added to this total over the next few days.

Rain and snow pelted southern California throughout the day Friday, leading to floods, mudslides and nightmarish traffic. The rain also caused a plane to skid off a wet runway at Hollywood Burbank Airport.

On Friday, the storm is forecast to ramp up in intensity as it moves across the southern U.S.: "Accumulating snow and ice appears likely from eastern New Mexico to western Oklahoma on Friday with snow totals of 4 to 8 inches, with locally higher amounts possible especially across the Texas Panhandle," weather service forecaster Allison Santorelli said.

"A swath of potentially significant ice is also forecast from roughly Lubbock, Texas, to near Oklahoma City, with accumulations in excess of 0.10 to 0.25 inches possible," she added. The Weather Channel warned that the ice accumulations could cause extensive power outages and tree damage.

Further to the south, very heavy rainfall and flooding will be a big threat with this storm, according to AccuWeather meteorologist Ryan Adamson. The heaviest rain and flood threat Friday is across southern Texas, where up to 10 inches of rain could swamp the flood-prone Houston area.

Gavin Keller, left, and Hunter Matthews work the clear snow from the walkway of a home in Richmond, Va., Monday, Dec. 10, 2018. A winter storm kept dumped immobilizing snow, sleet or freezing rain across several southern states, leaving dangerously icy roads and hundreds of thousands of people without electricity. Steve Helber, AP

A Duke Energy lineman uses a bucket truck to approach a transformer on Hope Valley Road in Durham, N.C. Sunday, Dec. 9, 2018 as heavy snow blankets the area. Power is out in many areas and local roads are almost impassible as the late fall snowstorm hit North Carolina. Chuck Liddy, The News & Observer, via AP

A man jogs with his dog down a snow-covered street in Greensboro, N.C., Sunday, Dec. 9, 2018. A massive storm brought snow, sleet, and freezing rain across a wide swath of the South on Sunday - causing dangerously icy roads, immobilizing snowfalls and power losses. Chuck Burton, AP

A car drives slowly down Old NC 98 in Wake Forest, N.C., on Sunday, Dec. 9, 2018. A storm spreading snow, sleet and freezing rain across a wide swath of the South has millions of people in its path, raising the threat of immobilizing snowfalls, icy roads and possible power outages. Allen G. Breed, AP

Tervante Wilkerson trudges through blowing snow up Old NC 98 in Wake Forest, N.C., on Sunday, Dec. 9, 2018. Wilkerson, who was walking across town to see his two young children, said, "It's definitely a Kodak moment in Wake Forest." Allen G. Breed, AP

This aerial photo taken from video provided by KABC-TV shows traffic at a standstill on Interstate 5 near Gorman, Calif., early Thursday, Dec. 6, 2018. The second storm in a week brought record-breaking rainfall to parched Los Angeles on Thursday, jamming traffic on Southern California highways and prompting evacuations in wildfire-scarred areas. KABC-TV via AP

A Southwest Airlines plane slid off the runway at Hollywood Burbank Airport, coming to a stop after its landing gears plowed into a barrier designed to stop the airplane from leaving the runway Thursday, Dec. 6, 2018, in Burbank, Calif. Nobody was hurt when the plane from Oakland skidded off the wet runway as it landed during downpours at the airport north of Los Angeles. Myung J. Chun, Los Angeles Times via AP

A Kentucky Department of Transportation vehicle sprays salt brine on Highway 45 South near Wingo, Kentucky on Thursday, Dec. 6, 2018. There is potential for a winter storm to hit western Kentucky this weekend. The system is expected to move in late Saturday through Sunday and Monday, but the exact areas of impact and extent of those impacts are still in question. Ellen O'Nan, The Paducah Sun via AP

A Malibu Public Works crew clears a culvert that overflowed with mud and debris on Cuthbert Road in an area burned by the Woolsey fire in Malibu, Calif. Thursday, Dec. 6, 2018. The second round of a fall storm is causing flooding on Los Angeles-area roads. Snow has forced the closure of Interstate 5 in the Grapevine area between LA and the San Joaquin Valley. Closer to sea level, the system dumped rain that flooded highways and caused nightmare traffic conditions for commuters. Reed Saxon, AP

Some severe thunderstorms could also rumble through the region: “The greatest risk of severe weather that includes the possibility of a few isolated tornadoes is over portions of central and South Texas on Friday afternoon and evening,” AccuWeather meteorologist Alex Sosnowski said.

By Saturday, the rain and flood threat will shift to most of the Deep South and Southeast. Along the northern edge of the storm, from Missouri to the Carolinas, more freezing rain and ice is likely.

The storm could save its worst for last: Late Saturday and through the day Sunday, it's forecast to paste the central and southern Appalachians with heavy snow, potentially crippling the region. "From central and western North Carolina to parts of southern West Virginia and southwestern and south-central Virginia, this will be a major storm with the potential for a foot or more of snow," according to AccuWeather meteorologist Brian Wimer.

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A driver in Kalamazoo, Michigan captured the moment his windshield was smashed by snow as a snowplow driver cleared an overpass. He's okay, but his windshield is not.
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Asheville, North Carolina, is forecast to pick up a foot of snow, which would place the storm on the city's list of biggest snowstorms on record.

After blasting the South, the storm should finally move east and off the East Coast by Monday and Tuesday, with little to no impact expected for the big cities of the Mid-Atlantic and Northeast. However, that forecast could still change as more recent weather information is fed into the computer models that help predict storm paths.